The present invention relates to an apparatus or assembly for mounting a vibrating body to a support structure. More specifically, the invention relates to a mounting device employing a fluid active mount to mount a body or mass subject to vibrational excitations to a frame or support structure, with damping or isolation of such excitations. The invention is particularly suitable for use in mounting an internal combustion engine to a motor vehicle frame or body.
In mounting a vibrating body to a support structure, such as in mounting an internal combustion engine to the frame or unibody of a motor vehicle, it long has been known to employ elastomeric block structures as mounting devices to provide isolation (reduced transmissibility) and/or damping of the vibrations generated by or induced in the body. Difficulty exists, however, in effectively damping or isolating the broad range of vibrational frequencies and amplitudes generated by an internal combustion engine. One significant difficulty lies in that the vibration damping provided by known elastomeric engine mounts varies proportionately with the transmissability of vibration by such engine mount. A relatively hard elastomer will provide good damping of high amplitude vibrations, but is relatively ineffective to damp low frequency low amplitude vibrations such as vibrations during engine idle. On the other hand, relatively soft elastomeric mounts, while better able to isolate low frequency low amplitude vibrations, would be relatively ineffective to damp or isolate higher amplitude vibrations.
An effective engine mounting device is needed, therefore, to damp or isolate a broad range of vibrational modes and a broad range of vibration frequencies and amplitudes. Thus, for example, an internal combustion engine will produce relatively low frequency, low amplitude torque pulses during engine idle. Larger amplitude torques are generated during clutch release and rapid acceleration. In addition, substantially vertical vibrational modes may include low amplitude, high frequency vibrations, such as those generated by powertrain deformations and second order unbalanced inertia forces typical in four cylinder engines. Also, large amplitude essentially vertical vibrations must be damped, such as those generated by large amplitude powertrain deflections and even externally caused vibrations such as those induced in a motor vehicle engine by the collision the vehicle's tires with road obstructions, potholes, etc. It is an object of the present invention to provide a mounting system which provides damping and isolation substantially effective for a broad range of vibrational amplitudes.
Known motor vehicle engine mounting systems and devices have proven unsatisfactory and, in particular, have not been sufficiently effective in damping or isolating the broad range of vibration frequencies and amplitudes generated in normal use of a motor vehicle. In U.S. Pat. No. 4,159,091 to LeSalver et al. is disclosed a damping device for suspension of a motor vehicle engine. The device is relatively complex, having two internal chambers, the first of which and at least a portion of the second of which chambers are filled with liquid, a partition wall with a calibrated orifice dividing the two chambers. A somewhat similar approach is suggested in U.S. Pat. No. 4,352,487 to Shtarkman, wherein a shock absorber is shown to have inner and outer rigid members connected by an elastomeric shear spring and having a main fluid chamber disposed between the two rigid members in fluid communication through a restricted orifice to a second fluid chamber within the inner rigid member. A third chamber is provided, specifically an elastomeric bladder within the second fluid chamber, which is selectively chargeable with gas pressure for calibrating the damping characteristics of the device. In addition, a fourth chamber is provided, specifically an elastomeric diaphragm is included in the main fluid chamber to provide a selectively chargeable gas chamber. Another elastomeric engine mount with hydraulic damping is shown in U.S. Pat. No. 4,161,304 to Brenner et al. The engine mount thereof includes an elastic peripheral wall joined with metallic end walls to form a liquid-filled main chamber and a liquid-filled auxiliary chamber. The two metallic end walls are rigidly connected. The peripheral walls function as thrust springs. The partition between the two liquid-filled chambers is said to be either rigid and stationery or moveable. An engine mount of this kind is said to be suitable to strongly damp lower frequency, high amplitude oscillations of the engine while allowing high frequency oscillations with low amplitude to pass undamped.
Early attempts were made to provide improved damping by interconnecting multiple engine mounts. Thus, for example, in U.S. Pat. No. 2,038,968 to Summers an engine mount is shown in which an elastomeric peripheral wall together with rigid end walls defines a fluid-filled chamber. A helical spring is embedded in the elastomeric wall for reinforcement and damping effect, while an additional damping mode is said to be provided by virture of a conduit providing fluid communication between the fluid-filled chamber of one and another such engine mount. A similar mounting system is suggested in U.S. Pat. No. 2,705,118 to Beck, wherein rigid supporting and supported members are interconnected by a body of resilient elastomer. The elastomeric body, together with the supporting member defines a fluid-filled chamber which is so designed as to expand or contract as the supported and supporting members vibrate toward and away from each other. The chambers are said to be filled with hydraulic brake fluid and it is suggested that damping of torsional vibration can be achieved by a fluid flow restrictor valve interposed in the connecting line between the liquid-filled chambers. U.S. Pat. No. 1,655,204 to Stevens is directed to a vehicle suspension means employing a fluid communication line between mounting devices.